This invention relates to a carburetor for an internal combustion engine, and more particularly to a carburetor equipped with a rotary throttle valve and adapted for being incorporated in a two-cycle engine used as a drive source for a chain saw, reaper, bush cutter or the like.
A carburetor equipped with a rotary throttle valve for an internal combustion engine has heretofore been proposed. In such a carburetor, the rotary throttle valve is turned to change a relative position of a venturi hole running across the throttle valve to an air hole provided in the carburetor body, to thereby vary an effective diameter of the air hole, whereby an amount of fuel being injected from a fuel nozzle disposed in the venturi hole is controlled. Such a carburetor successfully controls the usual running modes of an engine properly and highly responsively by turning the throttle valve.
When the throttle valve assumes an idling opening position, a flow rate of intake air passing through the venturi hole becomes low, thus decelerating atomization of a fuel, such that in the idling of the engine at a specific posture of the carburetor, smooth supply of the fuel from the nozzle to the internal combustion engine by the streams of air is incomplete, resulting in part of the fuel being accumulated in the venturi hole. Such a carburetor has an advantage of controlling the usual running modes excluding the idling, of an engine properly and highly responsively, irrespective of the posture of the carburetor, and on the other hand, is disadvantageously accompanied by the lowered performance at the idling of the engine at a specific posture of the carburetor. Particularly in the case where the carburetor valve is turned with the up side down from the aforesaid specific posture, the fuel accumulated in the venturi hole is abruptly drawn under suction into the internal combustion engine causing an overrich condition leading of the stopping of the engine.
Because of the above-described drawback, the prior art carburetor with a rotary throttle valve could not find applications to an internal combustion engine of a chain saw or defrosting instruments which must provide a good performance even at any posture of the carburetor, resulting in limitation in application.
It is an object of the present invention to provide a rotary-throttle-valve-type carburetor which is capable of controlling all of the running modes including the idling, of an internal combustion engine properly, even at any posture of the carburetor, with the freedom from the drawbacks of the prior art carburetor of the type.
One of the features of the present invention consists in the provision of a by-pass for guiding to the fuelair inlet of an internal combustion engine any fuel tending to accumulate in a venturi hole in a rotary throttle valve in certain positions of the engine. This prevents the fuel from being accumulated in the venturi hole and avoid a pocket of fuel which might be dumped into an engine upon a shift of posture of the engine to cause an overrich condition leading to stopping the engine.
This and other features of the present invention will be apparent from the description of the specification in conjunction with the accompanying drawings which indicate preferred embodiments of the invention.